I was googling around and seen some products that looked like they would work. Problem is the one I was looking at for 399.00 for music on hold only worked with 4 lines. Oh well...im sure there is something out there.

What you are getting with Vonage is a simple analog line, not a PBX station.

You don't have a way to tell Vonage that you are placing the line on hold with a standard analog line, because a standard analog line doesn't have the capability to communicate that fact back to the telco. In an analog phone, "hold" is simply leaving the line off-hook while muting both directions of the conversation.

So music would have to be handled by whatever device placed the call on "hold". This is normally built into the phone, and would simply feed music into the line when the "hold" button is pressed instead of the usual silence.

You can get phones or hold devices that introduce music locally, or if you have your Vonage lines feeding into a PBX of some sort, the PBX probably has a "music on hold" feature or one can be added.

You send it a signal to put the line on hold by pressing [*]. When the unit hears that signal, it keeps the line off-hook, cuts signal to your actual handset, and starts feeding music into the outgoing line. It then monitors your handset to see when you take it off-hook, at which point it connects the call back to your handset.

Plenty of devices like this exist, and I'm not recommending this one in particular - it just happened to be the first result in a Google search.